Process for the preparation of aldehydes

ABSTRACT

The invention relates to a process for the preparation of aldehydes in which at least one compound containing a vinyl or vinylidene group is reacted with carbon monoxide and hydrogen in the presence of a source of a metal from sub-group VIII and in the presence of a bidentate diphosphine ligand, where the diphosphine ligand has the general formula I                    
     in which 
     A together with the phosphorus atom to which it is bonded, in each case forms a 2-phosphatricyclo[3.3.1.1{3,7}]decyl radical, in which one or more non-adjacent carbon atoms may be replaced by oxygen atoms and which is substituted or unsubstituted, and 
     X is a bridging chain having 1 to 10 carbon atoms, 
     and the molar ratio between the diphosphine ligand and the metal is at least 5. The process gives predominantly n-aldehydes.

The present invention relates to a process for the preparation ofaldehydes in which at least one compound containing a vinyl orvinylidene group is reacted with carbon monoxide and hydrogen in thepresence of a source of a metal from sub-group VIII and in the presenceof a bidentate diphosphine ligand.

Hydroformylation or the oxo synthesis is an important large-scaleindustrial process and serves for the preparation of aldehydes byreaction of ethylenically unsaturated compounds with carbon monoxide andhydrogen. The reaction itself is highly exothermic and generallyproceeds under superatmospheric pressure and at elevated temperatures inthe presence of catalysts. The catalysts employed are usually metalsfrom sub-group VIII of the Periodic Table of the Elements, in particularcobalt, rhodium, iridium, ruthenium, palladium or platinum compounds orcomplexes, which may have been modified by means of nitrogen- orphosphorus-containing ligands in order to influence the activity and/orselectivity.

In the case of asymmetrical ethylenically unsaturated compounds, the twopossible orientations of the carbon monoxide adduction onto the C—Cdouble bond give different aldehydes. In general, therefore, a mixtureof isomeric aldehydes is obtained, as illustrated below.

The compound (1) is frequently known as n-aldehyde, and the compound (2)as iso-aldehyde.

Owing to the fact that the n-aldehydes are generally of significantlygreater industrial importance than the isoaldehydes, it is an aim tooptimize the hydroformylation catalysts and conditions in order toachieve the greatest possible n-selectivity, i.e. the highest possibleratio of n-aldehyde to isoaldehyde in the product aldehydes.

WO 98/42717 describes carbonylation reactions in the presence of acarbonylation catalyst containing a diphosphine, of which at least onephosphorus atom is part of a 2-phosphatricyclo[3.3.1.1{3,7}]decyl group.The carbonylation reactions described also include hydroformylations.Although WO 98/42717 indicates that, in order to prepare the catalystsystem described therein, the ligand is generally employed in excessrelative to the metal cation, nothing is stated regarding the amount ofligand present during the carbonylation reaction. In thehydroformylation examples in WO 98/42717, molar ratios between thediphosphine ligand and the rhodium metal of 1:1.2 (Example 9), 1:1(Example 10) and 1:2 (Example 11) are used. In the hydroformylation ofpropene, an approximately equimolar mixture of butanal and2-methylpropanal is obtained.

It is an object of the present invention to indicate a process with veryhigh n-selectivity for the preparation of aldehydes by hydroformylationof compounds containing at least one vinyl or vinylidene group.

We have found that this object is achieved by a process for thepreparation of aldehydes in which at least one compound containing avinyl or vinylidene group is reacted with carbon monoxide and hydrogenin the presence of a source of a metal from sub-group VIII and in thepresence of a bidentate diphosphine ligand, where the diphosphine ligandhas the general formula I

in which

A together with the phosphorus atom to which it is bonded, in each caseforms a 2-phosphatricyclo[3.3.1.1{3,7}]decyl radical, in which one ormore non-adjacent carbon atoms may be replaced by oxygen atoms and whichis substituted or unsubstituted, and

X is a bridging chain having 1 to 10 carbon atoms,

and the molar ratio between the diphosphine ligand and the metal is atleast 5.

The molar ratio between the diphosphine ligand and the metal is inaccordance with the invention at least 5, preferably at least 8 and inparticular at least about 10. The molar ratio is generally less thanabout 50, usually less than about 20.

Tricyclo[3.3.1.1{3,7}]decane is also known by the trivial name“adamantane”. In the 2-phosphatricyclo[3.3.1.1{3,7}]decyl radical of theligand used in accordance with the invention, one or more non-adjacentcarbon atoms, which are preferably not adjacent to the phosphorus atom,may have been replaced by oxygen atoms. The carbon atoms in positions 6,9 and 10 have preferably been replaced by oxygen atoms.

The 2-phosphatricyclo[3.3.1.1{3,7}]decyl radical may carry substituentson one or more of its carbon atoms. One or more carbon atoms inpositions 1, 3, 5 and/or 7, in particular all carbon atoms in positions1, 3, 5 and 7, preferably carry substituents, which are preferablyidentical. Examples of suitable substituents are alkyl, cycloalkyl,haloalkyl, aryl and aralkyl. The carbon atoms in positions 4 and/or 8may carry one or two substituents, such as C₁-C₄-alkyl or halogen atoms,in particular fluorine atoms.

The two 2-phosphatricyclo[3.3.1.1{3,7}]decyl radicals present in thediphosphine ligands to be used in accordance with the invention may haveidentical or different substituents. Depending on the substitutionpattern, the diphosphines may be in the form of diastereomers. Ingeneral, both the diastereomer mixtures and the pure diastereomers aresuitable for the purposes according to the invention.

X is a bridging chain having 1 to 10 atoms, preferably 2 to 4 atoms, inparticular 3 atoms. X is preferably a C₁- to C₁₀-alkylene bridge, whichmay have one, two, three or four double bonds and/or may be interruptedby one, two or three non-adjacent heteroatoms and/or may be fused toone, two or three saturated or unsaturated 3- to 7-membered carbocyclicor heterocyclic rings.

The fused unsaturated carbocyclic rings in radical X are preferablybenzene or naphthalene, in particular benzene. Fused benzene rings arepreferably unsubstituted or have 1, 2 or 3, in particular 1 or 2,substituents selected from alkyl, alkoxy, halogen, haloalkyl, nitro,carboxyl, alkoxycarbonyl and cyano. Fused saturated carbocyclic ringsare preferably cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl.

If the alkylene bridge in radical X is interrupted by heteroatoms, theseare preferably selected from oxygen, sulfur and nitrogen.

Preferred radicals X are selected from

—(CH₂)_(x)—

where x is an integer from 1 to 10, preferably 2 to 4,

Y is O, S or NR⁵, where R⁵ is alkyl, cycloalkyl or aryl,

or Y is a C₁-C₃-alkylene bridge, which may have a double bond and/or analkyl, cycloalkyl or aryl substituent,

or Y is a C₂-C₃-alkylene bridge which is interrupted by O, S or NR⁵,

R¹, R², R³ and R⁴, independently of one another, are hydrogen, alkyl,cycloalkyl, haloalkyl, aryl, alkoxy, aryloxy, aralkoxy, halogen, nitro,alkoxycarbonyl or cyano.

X is particularly preferably propylene.

A, together with the phosphorus atom to which it is bonded, ispreferably a group of the general formula II

where the radicals R, independently of one another, are alkyl,cycloalkyl, haloalkyl, aryl or aralkyl.

For the purposes of the present invention, the terms used have thefollowing meanings, unless stated otherwise:

“alkyl” means straight-chain or branched alkyl, preferably C₁-C₂₀-alkyl,in particular C₁-C₈-alkyl, particular preferably C₁-C₄-alkyl. Examplesof alkyl groups are, in particular, methyl, ethyl, propyl, isopropyl,n-butyl, 2-butyl, s-butyl, t-butyl, n-pentyl, 2-pentyl, 2-methylbutyl,3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl,2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl,3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl,2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl,3,3-dimethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl,1-ethylbutyl, 2-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl,3-heptyl, 2-ethylpentyl, 1-propylbutyl and octyl;

“cycloalkyl” preferably means C₅-C₇-cycloalkyl, such as cyclopentyl,cyclohexyl or cycloheptyl;

“haloalkyl” preferably means C₁-C₄-haloalkyl, i.e. a C₁-C₄-alkyl radicalwhich is partially or fully substituted by fluorine, chlorine, bromineand/or iodine, such as chloromethyl, dichloromethyl, trichloromethyl,fluoromethyl, difluoromethyl, trifluoromethyl, chlorofluoromethyl,dichlorofluoromethyl, chlorodifluoromethyl, 2-fluoroethyl,2-chloroethyl, 2-bromethyl, 2-iodoethyl, 2,2-difluoroethyl,2,2,2-trifluoroethyl, 2-chloro-2-fluoroethyl, 2,2-difluoroethyl,2,2-dichloro-2-fluoroethyl, 2,2,2-trichloroethyl, pentafluoroethyl,2-fluoropropyl, 3-fluoropropyl, 2,2-difluoropropyl, 2,3-difluoropropyl,2-chloropropyl, 3-chloropropyl, 2,3-dichloropropyl, 2-bromopropyl,3-bromopropyl, 3,3,3-trifluoropropyl, 3,3,3-trichloropropyl,2,2,3,3,3-pentafluoropropyl, heptafluoropropyl,1-(fluoromethyl)-2-fluoroethyl, 1-(chloromethyl)-2-chloroethyl,1-(bromomethyl)-2-bromoethyl, 4-fluorobutyl, 4-chlorobutyl, 4-bromobutyland nonafluorobutyl;

“aryl” preferably means C₆-C₁₆-aryl, such as phenyl, tolyl, xylyl,mesityl, naphthyl, anthracenyl, phenanthrenyl, naphthacenyl; inparticular phenyl or naphthyl;

“aralkyl” preferably means C₇-C₂₀-aralkyl, in particularphenyl-C₁-C₄-alkyl, such as benzyl or phenethyl;

“alkoxy” preferably means C₁-C₂₀-alkoxy containing an alkyl group,preferably as defined above;

“cycloalkoxy” preferably means C₅-C₇-cycloalkoxy containing a cycloalkylgroup, preferably as defined above;

“aryloxy” preferably means C₇-C₁₆-aryloxy containing an aryl group,preferably as defined above;

“aralkoxy” preferably means C₇-C₂₀-aralkoxy containing an aralkyl group,preferably as defined above;

and “halogen” means fluorine, chlorine, bromine or iodine, preferablyfluorine or chlorine.

The radicals R, independently of one another, are particularlypreferably C₁-C₄-alkyl, C₁-C₄-haloalkyl or phenyl, in particular methyl,t-butyl, trifluoromethyl or phenyl.

Particular preferred ligands include

1,2-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3,7}]decyl)ethane,

1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3,7}]decyl)propaneand

1,6-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decyl)hexane.

In order to prepare the diphosphine ligands of the formula I, a compoundcontaining 2 primary phosphine groups can, for example, be reacted witha 1,3-diketone, for example 2,4-pentanedione or substituted2,4-pentanediones, such as perfluoro-2,4-pentanedione or1,1,1,5,5,5-hexafluoro-2,4-pentanedione, with acid catalysis. Thecompounds of the formula I are generally obtained in high purity and canbe used directly without further purification. With respect to suitablereaction conditions, reference is made to J. Am. Chem. Soc. 1961, Vol.83, 3279-3282 and Chem. Com. 1999 (10, 1901-902) and WO 98/42717.

Im general, catalytically active species of the general formulaH_(x)M_(y)(CO)_(z)L_(q), in which M is a metal from sub-group VIII ofthe Periodic Table, L is a ligand of the general formula I, and q, x, yand z are integers depending on the valency and type of the metal, aregenerally formed from the catalysts or catalyst precursors employedunder hydroformylation conditions. The complexes may, if desired,additionally contain further ligands, which are preferably selected fromhalides, amines, carboxylates, acetylacetonate, aryl- andalkylsulfonates, olefins, dienes, cycloolefins, nitriles,nitrogen-containing heterocyclic compounds, aromatic compounds andheteroaromatic compounds, ethers, PF₃, and monodentate, bidentate andpolydentate phosphine, phosphinite, phosphonite and phosphite ligandswhich do not conform to the formula I.

The metal from sub-group VIII is preferably cobalt, ruthenium, rhodium,nickel, palladium, platinum, osmium or iridium and in particular cobalt,ruthenium, iridium, rhodium, nickel, palladium or platinum. Rhodium isthe most preferred. Suitable sources of said metals are generally theircompounds, for example salts, or complexes.

According to a preferred embodiment, the hydroformylation catalysts areprepared in situ in the reactor employed for the hydroformylationreaction. If desired, however, the ligand/metal complexes can also beprepared separately and isolated by conventional methods. For in-situpreparation, it is possible, for example, to react at least one ligandof the formula I, a compound or a complex of the metal from sub-groupVIII, if desired at least one further ligand and if desired an activatorwith carbon monoxide and hydrogen in an inert solvent underhydroformylation conditions.

Examples of suitable rhodium compounds or complexes are rhodium(II) andrhodium(III) salts, such as rhodium(III) chloride, rhodium(III) nitrate,rhodium(III) sulfate, potassium rhodium sulfate, rhodium(II) orrhodium(III) carboxylates, such as rhodium(II) and rhodium(III) acetate,rhodium(III) oxide, salts of rhodium(III) acid, trisammoniumhexachlororhodate(III), etc. Also suitable are rhodium complexes, suchas rhodium biscarbonylacetylacetonate,acetylacetonatobisethylenerhodium(I), etc. Preference is given torhodium biscarbonylacetylacetonate, rhodium acetate and rhodiumethylhexanoate.

Likewise suitable are ruthenium salts or compounds. Examples of suitableruthenium salts are ruthenium(III) chloride, ruthenium(IV),ruthenium(VI) and ruthenium(VIII) oxide, alkali metal salts of rutheniumoxygen acids, such as K₂RuO₄ or KRuO₄, or complex compounds, such asRuHCl(CO)(PPh₃)₃. It is also possible to use the metal carbonyls ofruthenium, such as trisruthenium dodecacarbonyl or hexarutheniumoctadecacarbonyl, or mixed forms in which some of the CO has beenreplaced by triorganophosphines, such as Ru(CO)₃(PPh₃)₂.

Examples of suitable cobalt compounds are cobalt(II) chloride,cobalt(II) sulfate, cobalt(II) carbonate, cobalt(II) nitrate, the amineand hydrate complexes thereof, cobalt carboxylates, such as cobaltformate, cobalt acetate, cobalt ethylhexanoate, cobalt naphthanoate, andcobalt/caprolactamate complex. Here too, it is possible to use thecarbonyl complexes of cobalt, such as dicobalt octacarbonyl, tetracobaltdodecacarbonyl and hexacobalt hexadecacarbonyl.

The above and other suitable compounds of cobalt, rhodium, ruthenium andiridium are known in principle and are described adequately in theliterature or can be prepared by the person skilled in the artanalogously to the compounds that are already known.

Examples of suitable activators are Brödnsted acids, Lewis acids, suchas BF₃, AlCl₃ and ZnCl₂, and Lewis bases.

Suitable substrates for the process according to the invention are inprinciple all compounds which contain one or more vinyl or vinylidenegroups. These include, for example, C₃-C₂₀-α-alkenes, in particularlinear C₃-C₂₀-α-alkenes, such as propene, 1-butene, 1-pentene, 1-hexene,1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, etc. Afurther preferred starting material is isobutene.

Other preferred starting materials are ω-nitrilo-C₂-C₂₀-alkenes, such asacrylonitrile and 4-pentene nitrile; andω-alkoxycarbonyl-C₂-C₂₀-alkenes, such as alkyl acrylates and alkyl4-pentenoates. Also suitable are vinyl aromatic compounds, such asstyrene and vinylpyridine.

The hydroformylation reaction can be carried out continuously,semi-continuously or batchwise. Suitable reactors are known to theperson skilled in the art and are described, for example, in Ullmann'sEnzyklopädie der technischen Chemie, Volume 1, 3rd Edition, 1951, pp.743 ff.

Carbon monoxide and hydrogen are usually employed in the form of amixture, so-called synthesis gas. The molar ratio between carbonmonoxide and hydrogen is generally from about 5:95 to 70:30, preferablyfrom about 40:60 to 60:40. In particular, a molar ratio between carbonmonoxide and hydrogen in the region of about 1:1 is employed.

The temperature during the hydroformylation reaction is generally in therange from about 80 to 180° C., preferably from about 100 to about 160°C. The reaction is generally carried out at the partial pressure of thereaction gas at the selected reaction temperature. In general, thepressure is in the range from about 5 to 200 bar, in particular from 5to 30 bar. The optimum temperature and the optimum pressure aredependent on the unsaturated compound employed.

The catalytically active ligand/metal complexes can be separated offfrom the hydroformylation reaction product by conventional methods knownto the person skilled in the art and can generally be re-employed forthe hydroformylation, if necessary after work-up.

In the hydroformylation, solvents can be used concomitantly, such as thehigh-boiling secondary-reaction products of the aldehydes formed in thehydroformylation. Other suitable solvents are aromatic hydrocarbons,such as toluene and xylene, aliphatic hydrocarbons, ethers, such as2,5,8-trioxanonane, diethyl ether and anisole, sulfones, such assulfolane, or esters, such as 3-hydroxy-2,2,4-trimethylpentyl1-isobutyrate (Texanol).

By means of the process according to the invention, n-selectivities ofgreater than 80%, in particular greater than 90%, are generallyachieved. The invention is illustrated in greater detail by thefollowing, non-restrictive examples:

EXAMPLES

The ligands were synthesized as described in WO 98/42717. Theabbreviation “acac” stands for acetylacetonate; L:M stands for the molarratio between the ligand and metal. The reaction mixtures obtained inthe examples were analyzed by gas chromatography (GC).

Comparative Example 1 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 1.65 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M 1:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 94%, the aldehyde selectivity was11%, the internal olefin selectivity was 89%. The molar ratio betweenn-nonanal and isononanal was 45:55.

Comparative Example 2 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 2.47 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M=1.5:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 83%, the aldehyde selectivity was12%, the internal olefin selectivity was 88%. The molar ratio betweenn-nonanal and isononanal was 43:57.

Comparative Example 3 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 3.3 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M=2:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 83%, the aldehyde selectivity was10%, the internal olefin selectivity was 90%. The molar ratio betweenn-nonanal and isononanal was 44:56.

Comparative Example 4 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 4.9 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M=3:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 85%, the aldehyde selectivity was27%, the internal olefin selectivity was 73%. The molar ratio betweenn-nonanal and isononanal was 72:28.

Comparative Example 5 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 6.6 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M=4:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 85%, the aldehyde selectivity was25%, the internal olefin selectivity was 75%. The molar ratio betweenn-nonanal and isononanal was 75:25.

Example 6 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 8.2 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M=5:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 100%, the aldehyde selectivitywas 69%, the internal olefin selectivity was 31%. The molar ratiobetween n-nonanal and isononanal was 97:3.

Example 7 Hydroformylation of 1-octene using1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decylpropane

0.9 mg of Rh(CO)₂acac and 16.4 mg of1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]-decylpropane(60 ppm of Rh, L:M=10:1) were dissolved separately in a total of 3 g oftoluene, mixed and aerated at 100° C. with 10 bar of synthesis gas(CO:H₂=1:1). After 30 minutes, the pressure was released, 3 g of1-octene were added, and the mixture was hydroformylated for 4 hours at100° C. and 10 bar. The conversion was 80%, the aldehyde selectivity was95%. The molar ratio between n-nonanal and isononanal was 97:3.

The examples show that the proportion of n-aldehyde in the aldehydesobtained is significantly higher at a ligand:metal molar ratio of atleast 5 than at lower ligand:metal molar ratios.

We claim:
 1. A process for the selective preparation of n-aldehydes inwhich at least one compound containing a vinyl or vinylidene group isreacted with carbon monoxide and hydrogen in the presence of a source ofa metal from sub-group VIII and in the presence of a bidentatediphosphine ligand, where the diphos-phine ligand has the generalformula I

in which A together with the phosphorus atom to which it is bonded, ineach case forms a 2-phosphatricyclo[3.3.1.1{3,7}]decyl radical, in whichone or more non-adjacent carbon atoms may be replaced by oxygen atomsand which is substituted or unsubstituted, and X is a bridging chainhaving 1 to 10 carbon atoms, and the molar ratio between the diphosphineligand and the metal is at least
 5. 2. A process as claimed in claim 1,where X is a C₁-C₁₀-al-kylene bridge, which may have one, two, three orfour double bonds and/or may be interrupted by one, two or threenon-adjacent heteroatoms and/or may be fused to one, two or threesaturated or unsaturated 3- to 7-membered carbocyclic or heterocyclicrings.
 3. A process as claimed in claim 1, where the molar ratio betweenthe diphosphine ligand and the metal is at least
 8. 4. A process asclaimed in claim 2, where A, together with the phosphorus atom to whichit is bonded, is a group of the general formula II

in which the radicals R independently of one another, are alkyl,cycloalkyl, haloalkyl, aryl or aralkyl.
 5. A process as claimed in claim4, where the ligand is selected from 1,2-P, P′-di (2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decyl)ethane,1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decyl)propaneand1,6-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3,7}]decyl)hexane.6. A process as claimed in claim 1, where X is a three-atom chain.
 7. Aprocess as claimed in claim 1, where the compound containing a vinyl orvinylidene group is selected from C₃-C₂₀-α-alkenes, isobutene,ω-nitrilo-C₂-C₂₀-alkenes and O-alkoxycarbonyl-C₂-C₂₀-alkenes.
 8. Aprocess as claimed in claim 1, where the metal from sub-group VIII isrhodium.